1. Field of the Invention
The present invention relates to a sealing structure suitable for use in rotary type electrical parts such as rotary type variable resistors and rotary switches.
2. Description of the Related Art
Rotary operation type electrical parts are finding wider use in various fields. It often happens that a vehicle, for example, is provided with an electrical device referred to as a throttle position sensor in order to set the optimal amount of feeding of fuel according to the running speed of the vehicle and to run the vehicle at the optimal fuel consumption. One type of throttle position sensor, that includes a sliding-element receiver to which sliding elements are attached is connected to a rotary shaft and is rotated according to the degree of depression of an accelerator pedal in such a way that they are rotated integrally with each other. The degree of rotation of the rotary shaft corresponding to the degree of depression of the accelerator pedal is detected as variations in resistance values by providing a substrate having a resistance body and a collecting body both formed onto the surface thereof in an opposing relationship to the sliding-element receiver and bringing the sliding elements into sliding contact with the resistance body and the collecting body.
This type of throttle position sensor is disclosed in Japanese Utility Model Application Laid-Open No. 62-47104, for example. FIG. 4 is a fragmentary cross-sectional view of a throttle position sensor. FIG. 5 is a plan view of a cover.
Referring to FIG. 4, designated at numeral 1 is a case which forms a casing for the throttle position sensor. The case 1 is fixedly mounted in a bonnet of a vehicle, for example. An accommodating portion 2 for accommodating respective members which constitute a rotary type variable resistor is defined in the case 1. In addition, an opening 3 for the attachment of the respective members is defined in one side of the accommodating portion 2.
An attachment hole 4 is defined in a position opposite to a position where the opening 3 of the case 1 is defined. A bearing bush 5 is inserted into and fitted in the attachment hole 4. In addition, a driving shaft 6 is rotatably inserted into and fitted in the bearing bush 5. One end of the driving shaft 6 extends outwardly of the case 1 and is connected to an accelerator pedal (not shown) so as to be rotated by the degree of rotation thereof corresponding to the degree of depression of the accelerator pedal. In addition, the other end of the driving shaft 6 extends in the accommodating portion 2 and is mounted so as to be rotatable integrally with a sliding-element receiver 7. Sliding elements 8a, 8b are mounted on the surface of the sliding-element receiver 7. Each of the sliding elements 8a, 8b is brought into sliding contact with a resistance body 10a and a collecting body 10b both formed onto the surface of a substrate 9 provided in an opposing relationship to the sliding-element receiver 7.
Designated at numeral 11 is a cover for covering the opening 3 of the accommodating portion 2. The cover 11 is comprised of an insulating material such as synthetic resin, etc. The substrate 9 is positioned by fitting the cover 11 onto the opening 3 in a state in which the substrate 9 is brought into sliding contact with a step portion 1a formed on an inner-wall face of the case 1. The sliding-element receiver 7 is urged by a wave washer 12 in a direction in which the respective sliding elements 8a, 8b thereof are brought into sliding contact with the resistance body 10a and the collecting body 10b respectively. Therefore, the sliding elements 8a, 8b are brought into sliding contact with the resistance body 10a and the collecting body 10b, respectively, in a good condition. The cover 11 has a ventilating cylinder 13 which projects from the outer peripheral wall of the cover 11. The axial length of the ventilating cylinder 13 is set in such a manner that the tip portion of the ventilating cylinder 13 slightly projects from an open end of the opening 3 in the case 1. As shown in FIG. 5, an air passage 14 is defined in the inner side face of the cover 11. In addition, one side end of the air passage 14 communicates with an air-flow passage 16 defined inside the ventilating cylinder 13 by way of a through-hole 15, whereas the other side end thereof communicates with the accommodating portion 2 by way of a concave portion 17. A resin well 18 is formed in the course of the air passage 14. The air passage 14 is divided into a passage portion 14a directed from the well 18 to the side of the ventilating cylinder 13 and a passage portion 14b directed to the side of the concave portion 17. In the present embodiment, the passage portion 14a is placed at an angle of 90.degree. with respect to the passage portion 14b.
Furthermore, holes 20 for guiding air take-out terminals 19 connected to both ends of the resistance body 10a and the collecting body 10b into the outside are defined within the concave portion 17 of the cover 11. The take-out terminals 19 are electrically connected to their associated signal lines 21 at the outside of the cover 11, and the respective signal lines 21 are inserted into a take-off insulator 22.
Designated at numeral 23 in the drawing is a thermosetting filler material such as epoxy resin. The filler material 23 is charged into a region between the inner-wall face of the case 1 and the outer periphery of the ventilating cylinder 13 in such a manner that the outer peripheral wall of the cover 11 is covered with the filler material 23, thereby sealing between the outer peripheral wall of the cover 11 and the inner-wall face of the case 1, and the holes 20. In addition, the filler material 23 serves to protect the terminals 19 and the signal lines 21 connected thereto from conducting in a state in which they are embedded therein. Further, designated at numeral 24 is a hot-melt injection material comprised of melt thermoplastic resin injected into the ventilating cylinder 13. Thus, the inside of the ventilating cylinder 13 is sealed by the hot-melt injection material 24, and the accommodating portion 2 in the opening 3 of the case 1 is structurally held in a tightly-sealed manner by making use of the thermosetting filler material 23 and the hot-melt injection material 24.
Finally, designated at numeral 25 in the drawing is a sealing member for sealing tight between the bearing bush 5 and the driving shaft 6.
The structure of the above-described conventional arrangement has the problem in that since the thermosetting filler material 23 must be charged into the region between the inner-wall face of the case 1 and the outer peripheral wall of the ventilating cylinder 13, and the hot-melt injection material 24 must be charged into the ventilating cylinder 13, two steps are required, thereby causing poor workability. In addition, the airtightness cannot be checked after the hot-melt injection material 24 is charged into the ventilating cylinder 13 in the above-described manner.